The present invention relates to a process of tire manufacture and assembly drums serving to practice the process.
The invention relates more specifically to the manufacture of tires comprising a casing carcass and at least one reinforcing bead wire in each of the beads, around which the casing carcass is rolled forming a fold such that, contrary to common practice, the fold of the casing carcass is arranged between the bead wire and the casing carcass itself.
Some manufacturing processes employ assembly drums comprising shoulders, in particular, against which the wire is brought by describing an axial movement. The wire is held against the shoulder by simple adhesion between the materials or by an additional means. Such drums may employ bead wires directly, or separately fabricated semifinished products consisting of the bead wire surmounted radially by a section of rubber composition. Hereinafter, the term xe2x80x9cbead wire complexxe2x80x9d will be used to mean a bead wire alone, a bead wire surmounted by a section of rubber composition, optionally further comprising a coating compound for the bead wire filler such as another rubber composition section or a rubber ply comprising cords.
By way of example, mention may be made of publication FR 1,397,751, describing such an assembly drum with shoulders having a single working position, non-expanding, for rolling the casing, and a (radially) retracted position for axially extracting the tire casing produced. The bead wire complexes are laid on each shoulder during fabrication of the casings respectively and held in place by an axially displaceable accessory means.
Such drums serve for tire fabrication by process steps consisting of:
Positioning the casing carcass on the drum with its ends axially passing beyond the surface of the drum,
Applying said ends against the shoulders of the drum, generally with the aid of axially displaced depressing fingers,
Then positioning the bead complexes against the shoulders of the drum,
Finally, actuation of folding means generally consisting of inflatable envelopes to lift the ends of the casing carcass and thus fold the carcass around said complexes without changing their positioning.
Thus it is not possible, with such drums, to arrange the fold of the casing carcass between the bead and the carcass itself. Actually, this method cannot fold the ends of the casing carcass under the bead complexes when the latter are already in position against the casing.
The object of the invention, then, is to manufacture a tire by using bead wire complexes in which the casing carcass fold is positioned between the bead wire and the said casing carcass.
According to the invention, the tire manufacturing process comprises the following steps:
Laying a casing carcass on a generally cylindrical main receiving surface, at least one side end of the casing carcass being laid vertically to and overhanging a first cylindrical support surface coaxial with and of smaller diameter than the main receiving surface,
laying a rubber composition section on said end of the casing carcass,
folding said end around the rubber composition section, while keeping the said section substantially stationary,
laying a bead wire complex on the fold so made and axially to the inside of the place where the section is laid.
In practice, the two sides of the drum are designed alike, so that the other one of the lateral ends of the casing carcass is likewise placed vertically to and overhanging another first cylindrical support surface, arranged axially on the other side, likewise coaxial with and of smaller diameter than the main receiving surface.
Advantageously, the folding of the end of the casing carcass around the rubber composition section is performed:
By lifting said end radially so that it is oriented substantially radially,
Then bringing the bead wire complex axially towards the center of the casing carcass until the casing end rests on the bead wire complex
And continuing the axial approach of the bead wire complex, which passes over the rubber composition section.
More specifically, the end of the casing carcass is lifted radially by pressing radially outward in an area of said end located axially outside the rubber composition section.
Further, the invention proposes a process for manufacturing a tire, comprising the following steps:
Laying a casing carcass on a generally cylindrical main receiving surface, at least one of the side ends of the casing carcass being laid vertically to a first cylindrical support surface coaxially with the main receiving surface.
Laying a section of rubber composition on said end of the casing carcass.
Folding said lateral end around the section of rubber composition while keeping said section substantially stationary.
Laying a bead wire complex on the folds so made, axially to the interior of the place where the section is laid.
As mentioned above, in practice, the two lateral ends of the casing carcass are subjected to manipulations, if not identical at all points (since it may be that tires are to be produced whose bead wire diameters are not the same in each fold), at least similar in principle.